1. Summary of the Invention
The present invention relates to a warning device for a vehicle and trailer coupling system, and, in particular, to a warning device that provides a vehicle operator with information regarding the coupling condition of the coupling system, thereby alerting the operator when the vehicle and trailer are not properly coupled.
2. Background of the Invention
Conventional tractor-trailer combinations are coupled together by linking a kingpin, which is a cylindrical-shaped rod extending from the bottom of the trailer, to a fifth wheel, which is a plate pivotably mounted on the tractor. Coupling is achieved by positioning the tractor under the trailer such that the kingpin enters a V-shaped channel in the fifth wheel. A latching mechanism associated with the fifth wheel engages the kingpin, locking it within the crotch of the V-shaped channel.
To safely operate the tractor-trailer combination, the kingpin must be properly engaged by the latching mechanism during coupling and must not become disengaged during transit. Several devices are known for alerting the tractor-trailer operator that the kingpin is not properly positioned and/or locked within the fifth wheel. U.S. Pat. No. 3,697,979 to Harris et al., U.S. Pat. No. 3,535,679 to Connors and U.S. Pat. No. 2,387,628 to Walther et al. are examples of such devices.
Harris teaches a warning device having a first spring-biased mechanical switch located at the crotch of the fifth wheel channel and a second spring-biased mechanical switch located along the side of the channel. If the latching mechanism prematurely closes during coupling or opens thereafter, the switches close, thereby energizing a series connected lamp 14 (see FIG. 1 of Harris). Connors teaches a signalling mechanism having a first spring-biased mechanical switch that actuates with the movement of a hook-type latching mechanism and a second spring-biased mechanical switch that actuates when the fifth wheel pivots from horizontal. If the tractor and trailer are not properly coupled or have become uncoupled, the switches serially connect a power supply to a lamp 35 and buzzer 34 (see FIGS. 6-8 of Connors). Walther teaches a warning device including a single spring-biased mechanical switch actuating with the movement of pivotable jaws that hold the kingpin within the fifth wheel. Lamp 54 (see FIG. 5 of Walther), which is connected in series with the switch, is lit when the jaws are closed and is extinguished when the jaws are opened.
All of the above-described signalling devices employ spring-biased mechanical switches. Mechanical switches, however, wear out over a period of time and are susceptible to mechanical failure, especially in the harsh operating environment under the tractor-trailer fifth wheel. Additionally, debris from the road and/or grease from the tractor-trailer coupling system can interfere with the operation of the mechanical spring and/or prevent adequate electrical contact in the switch.
Furthermore, the above-described warning devices do not provide different signals to the operator that correspond to the different coupling conditions between the vehicle and trailer. For example, it is not possible for an operator viewing the binary output of the above devices to determine whether the latching mechanism has recently unlocked or has been unlocked for an extended period of time.
Finally, the above-described warning devices do not permit the operator to readily determine whether the device is operational unless the latching mechanism actually unlocks. As a result, there is a danger that the operator will assume that the lamp has not been activated because the vehicle and trailer are properly coupled, when, in fact, the lamp is burnt out.